The present invention relates generally to improved protected graphics and methods related to the same, which graphics and related methods are particularly useful for application to vehicles according to an exemplary aspect of the invention.
Graphical images (also referred to simply as “graphics”) take many forms and are used to provide desired textual or pictorial representations on a surface. A wide variety of materials are used to create graphical images on a surface, and graphics can generally be applied to a wide variety of surfaces. With that in mind, graphic designers face many challenges. A primary challenge is associated with successful application of a graphical image having a desired quality on a surface. Another challenge is associated with maintaining those applied graphics over time. As an example, materials used to create graphical images on a surface are prone to fading when exposed to radiation such as that in ultraviolet (UV) light. Mechanical (e.g., abrasive) or chemical contact with graphical images also tends to degrade such graphics over time. Quality of a graphical image is often balanced against a competing interest in permanence of that image.
In order to increase permanency of graphical images, ink used to create such images is often formulated with additives that improve mar resistance or other performance properties of the ink. Such additives include, for example, silicones and other low surface energy materials. A problem arising from the use of such relatively low surface energy additives, however, is the tendency of low surface energy additives to decrease the adherence of the inks to many substrates. Thus, while the ink itself may be improved with respect to its ability to resist degradation, the ink may not adequately adhere to the surface on which it is printed to form a graphical image, which can affect both the quality and the permanence of the image.
Another attempt to increase permanency of graphical images is application of the graphics under a film such that the graphics are outwardly visible, but yet protected, on a surface. Using this approach, graphics can be printed on a polymer film and adhered to a surface such that the graphical image lies between the polymer film and an underlying surface. The types of polymer films conventionally used in this approach are generally polyesters or fluoropolymers. Quality of the graphical image is often compromised, however, as the visual quality of the polymer film is generally not sufficient to allow undistorted viewing of the underlying graphics.
Further, conventional inks used to form such graphical images, which often have low surface energy additives as discussed above, often do not adequately adhere to adjacent polymer films or the low surface energy of an adjacent polymer film, such as a fluoropolymer film, can impair such adherence. Adherence is not only a factor as far as maintenance of graphics on a surface is concerned, but it is also a factor associated with ease of removability of such graphics when desired. For example, as team sponsorship or other insignia placed on a race car or other transportation vehicle changes, it is often desirable to easily remove outdated graphics from a vehicle's surface so that updated graphics can be applied in their place. When the graphics are part of an assembly containing multiple layers, interlayer delamination associated with inadequate adherence between layers can complicate the removal process.
A further consideration associated with protecting graphics with a polymer film overlay is weight associated with the polymer film. Particularly in the transportation industry, additional weight may lead to consumption of excess fuel and restrictions on the number of passengers or amount of cargo that an associated vehicle can safely and efficiently transport. Additional weight can also compromise operation of high performance vehicles, such as race cars. For example, as weight restrictions are often imposed on race cars, additional weight associated with surface paint or film decreases the amount of weight that can be strategically positioned elsewhere on the vehicle—such as in areas designed to increase the downforce (i.e., the downward pressure created by the aerodynamic characteristics of a car that allows it to travel faster through a corner by holding the car to the track or road surface) and, hence, performance of a race car. In particular, NASCAR's “Car of Tomorrow” is highly standardized, with more than two-hundred defined points that must be adhered to when designing a race car. Impacted by these new standards is aerodynamics of the race car. Making race cars wider and taller according to the new standards typically results in a corresponding sacrifice in aerodynamics, resulting in a slower average speed for the race car on a track. Thus, optimizing aerodynamic performance of a race car, which is impacted by the geometry and materials associated with a vehicle's surface, is highly desirable and of increasing concern.
Specific examples of some of the foregoing approaches to protecting graphics are now described. In setting forth the background of their teachings, U.S. Patent Publication No. 20070036929 (Boeing) describes how a conventional decal system (typically having a thickness of around 5 mils (125 microns)) consists of a clear polymer film provided to a printer, who prints graphics on the bottom side of the film, then applies pressure-sensitive adhesive.
According to the disclosure of this Boeing patent publication, thin film appliqués are prepared for application to aircraft and, after their application, include a polymer film, a pattern layer, a pressure-sensitive adhesive, and an overlying clearcoat. Polymer films described therein are urethane, acrylic, epoxy, vinyl, or polyester and have a thickness of between 0.5 mil (13 microns) and 1.0 mil (25 microns). Pattern layers, which may embody graphics, are said to be formed from acceptable commercial-off-the-shelf inks, including pigmented acrylic ink, pigmented fast-dry acrylic ink, urethane ink with pigment, epoxy ink, and urethane enamel coating such as DESOTHANE brand coatings (available from PRC Desoto International, Inc. of Glendale, Calif.). The systems therein are described as being applicable to an aircraft skin, after which time edge sealer (e.g., a clearcoat) is applied around its borders. The clearcoat is substantial, having a thickness equalized toward a combined thickness of the remaining layers—i.e., the polymer film, the pattern layer, and the pressure-sensitive adhesive. The clearcoat is said to provide a smooth finish, a high gloss on the order of around 80-90 gloss units, and resistance to impacts and degrading fluids. However, the systems described in the Boeing patent publication are often not able to protect surfaces from damage arising from surface impact with stones and other debris, such as that hazardous debris often encountered by race cars during a race. Further, the need for a clearcoat in order to obtain desired gloss on the outer surface undesirably increases weight of the assembly.
PCT Patent Publication No. WO2007/048141 (entrotech composites, IIc; GLF Ref. No. entrotech 06-0002) describes how, when printed material is included on an exterior surface of a composite article, addition of a protective coating after application of the printed material on the surface is not required. Any printed material desired to be placed on an exterior surface of a composite article is pre-printed onto a protective sheet prior to its bonding to the underlying composite article. The protective sheet is then applied to the surface of an underlying composite article such that the printed material is outwardly visible. Protective sheets described therein have enhanced durability (e.g., abrasion resistance), impact resistance, and fracture toughness and are stated to be useful in a range of indoor and outdoor applications—for example, the transportation, architectural and sporting goods industries. However, as the protective sheets described therein are integrally bonded to the underlying surface, they are not easily removable from such surfaces or capable of being selectively applied to, for example, a race car's surface after manufacture and assembly of the car. Similar restrictions are associated with the graphic image fusion in-molded and extruded parts described in U.S. Pat. No. 7,166,249 (Abrams et al.).
U.S. Pat. No. 7,048,989 (3M Innovative Properties Co.) describes sheeting that may comprise a graphic. The graphic may be exposed on the viewing surface of the sheeting or disposed between a topcoat and the viewing surface of the sheeting. The topcoats are typically digitally printed by at least one method selected from laser printing, ink-jet printing, and thermal mass transfer printing. The topcoat is preferably reverse-imaged and then disposed such that the image is between the topcoat and a retroreflective core. It is stated that the retroreflective sheeting having the water-borne acrylic based topcoat may be used for a variety of uses such as traffic signs, license plates, pavement markings (e.g., raised pavement markings), personal safety, vehicle decoration and commercial graphics such as retroreflective advertising displays, bus wraps, etc.
U.S. Pat. No. 7,141,294 (3M Innovative Properties Co.) describes a decorative film using no appreciable amount, or no amount, of polyvinyl chloride. This decorative film comprises a substrate, an adhesive layer for sticking the decorative film to an adherend formed on one surface of the substrate, a printed layer provided with a printed decorative pattern or character information formed on the other surface of the substrate, and a top clear layer for protecting the printed layer. The substrate is formed from an ethylene-(meth)acrylic acid copolymer. The top clear layer used as an outer-most layer is preferably made of a material that is superior in weatherability and water resistance and has high transparency (e.g., colorless coating compositions such as fluororesins, thermosetting urethanes, and ultraviolet-curing compositions). The decorative film is described as having flexibility for adhering, ink adhesion, water resistance, and weatherability with good balance. It is also described as being suitable for various adherends, particularly for adhering to buildings or vehicles used outdoors, including curved surfaces such as the body of vehicles.
Despite the number of methods conventionally used for application and maintenance of graphics of the desired quality, improvements in that regard are desired. For example, it would be desirable to provide a film comprising protected graphics without requiring additional layers to protect the graphics or enhance gloss value of the underlying layers within the film. Particularly in the race car industry, such a film would facilitate obtainment of the ever-desired optimized aerodynamic performance.